Jan. 18, 2011 -- Genes may link both your family and your friends, according to a new study.

Researchers found genetic links among groups of friends that suggest people tend to form friendships with others who share at least some genetic markers with them.

“People's friends may not only have similar traits, but actually resemble each other on a genotypic level,” write researcher James H. Fowler, of the division of medical genetics at the University of California, San Diego and colleagues, in the Proceedings of the National Academy of Sciences.

In two separate groups, one comprised of adolescents and the other adults, researchers found correlations in two of six genetic markers tested in those who forged friendships.

The study showed those who carried the DRD2 genetic marker, which has been previously associated with alcoholism, tended to form friendships with others who shared the same marker. Similarly, those who lacked this gene formed friendships with others who also did not have the gene.

Researchers say this finding supports the notion that people are attracted to others with similar traits -- the “birds of feather flock together” theory.

In contrast, a second genetic correlation provided evidence to support the belief that “opposites attract.” The results showed that people who had a gene associated with an open personality, CYAP26, tended to have friends who did not share this gene.

Researchers say together these results could have important implications in explaining the role genes play in shaping human behavior.

“For example, a person with a genotype that makes her susceptible to alcoholism may be directly influenced to drink,” write the researchers. “However, she may also be indirectly influenced to drink because she chooses friends with the same genotype.”